Conventionally, so-called compact disks (hereinafter referred to as CDs) have been used widely, on which successive data such as music information is recorded as digital signals in the form of optically detectable minute pits. The information on the CDs is reproducible through CD players for only reproduction.
FIG. 18 and FIG. 19 are schematic views illustrating a signal format to be used in the CDs. As shown in FIG. 8, a frame 31a of a recording signal is composed of a frame synchronization signal 31b indicating the leading portion of the frame, a sub-code 31c (described later) which is additional information of data, and a data field 31d comprising 24 bytes of main data and 8 bytes of error detection and correction parity added thereto. Errors in the data field 31d are detected and corrected based on an error detection and correction method employing a non-complete interleaving method, called Cross Interleaved Reed Solomon Code (CIRC).
As shown in FIG. 19, sub-codes 31c of 98 frames form a sub-coding block 32c. The 98 frames form a sector 32a (one sub-cording frame). Track numbers (the numbers of pieces of music if the data is music information) and absolute address information on the disk are determined based on the sub-coding block 32c. A frame synchronization signal 32b and a data field 32d respectively include 98 frames of the synchronization signals 31b and data fields 31d of FIG. 18.
If the length of the sector 32a, i.e. a sector length, equals for example 13.3 (ms), 75 sectors equal one second. In this case, sector numbers on the disk can be described as a function of time, "minute": "second": "a sector number in one second" (i.e. taking a value from 0 to 74), and the sector numbers form time information and address information which consecutively increase from the innermost portion outward of the disk.
FIG. 17 is a typical depiction illustrating an area allocation on the CD. A disk 33 comprises a main information recording area 33a and a Table Of Contents (TOC) area 33b (shown by hatching for convenience' sake). The main information recording area 33a stores main information such as music information and sub-code sector numbers, and the TOC area 33b stores sub-code additional information relating to respective information recorded in the main information recording area 33a, such as the track number and the recording start sector number of each track.
According to the format, when the disk 33 is placed into the CD player, sub-code information in the TOC area 33b is read and then the number of main information (equivalent to the number of music pieces in the case of music information) and sector numbers indicating the recording start positions of the respective information are recognized. Access to a desired track is promptly carried out upon receiving instructions to perform reproduction operation by verifying that the sub-code information read out from the TOC area 33b coincides with the sub-code sector number recorded in the main information recording area 33a.
In the CD, since information is recorded using the Constant Linear Velocity (hereinafter referred to as CLV) method, the recording density is uniform independently of any radial location on the disk 33, thereby permitting the recording volume to increase. During reproduction by the CD player, actually the CLV control is achieved by, for example, controlling the rotation of the disk 33 so that the interval of the frame synchronization signals in a reproduced signal from the CD recorded in the signal format equals a reference value.
In the mean time, in case various types of information including music information and computer information are recorded on rewritable optical disks such as magneto-optical disks having been developed recently, it is desirable to provide an information recording and reproducing device having compatibility of reproduction method with the conventional CDs and Compact Disk Read Only Memory (CD-ROM).
In this case, especially, for an optical disk whereon no information is recorded, absolute addresses using a sub-code in the signal format for CD and frame synchronization signals which can be used for the CLV control do not exist. Consequently, access operations to desired sectors can not be executed before recording operations and the CLV control required during recording and reproduction can not be achieved.
To counteract the above problem, the following method for recording absolute addresses without using sub-codes was suggested. In this method, absolute addresses go through a bi-phase mark modulation process, and guiding grooves of an optical disk are deviated inward or outward in a radial direction of the disk or the widths of the guiding grooves are varied according to "0" or "1" of the respective bits (see U.S. Pat. No. 4,907,216).
In the method, if the frequency band of absolute addresses having gone through the bi-phase mark modulation process varies from the frequency band of recording information having gone through the Eight to Fourteen Modulation (EFM) process, it is possible to reproduce them individually. In addition, access operations to portions wherein no recording information is contained can be performed by using the absolute addresses which were recorded by, for example, deviating the guiding grooves of the disk. As for the CLV control, an accurate velocity control is fulfilled by using reproduction carrier components of the absolute addresses, and the CLV control can also be performed in recording operations.
Rewritable optical disks having compatibility with CDs are expected to be used, especially in typical families, as high-density information recording media whereon various kinds of information such as music, text and image information can be recorded.
For example, the rewritable optical disks may be used as recording media for electronic still cameras, whereon voice information can be recorded.
Conventionally, electronic still cameras having an ability to record some comments on each still picture, use so-called floppy disks as recording media. Therefore, in case rewritable optical disks are used as recording media, image and voice information may be allocated on the disks in the same way as the floppy disks.
As shown in FIG. 20, in a method for allocating image and voice information, image information recording areas I1, I2 . . . (the volume as a function of time is, for example three to four seconds per picture) and voice information recording areas A1, A2 . . . (for example about ten seconds per picture) can be allocated alternatively in the recording area, and the capacity of the respective voice information recording areas A1, A2 . . . per picture can be fixed.
In this case, however, some problems may arise, for instance, the utility factor of the information recording areas A1, A2 . . . decreases when the actual voice information is shorter than the information recording areas A1, A2 . . . or on the contrary the actual voice information can not be stored in the respective information recording areas. Especially, when no voice information is recorded, the utility factor drops to a large degree.
To counteract the above kind of problem, as shown in FIG. 21, the image information recording areas I1, I2 . . . and the voice information recording areas A1, A2 . . . are allocated alternatively and the capacity of the voice information recording areas A1, A2 . . . is varied, so that desired length of voice information can be recorded for each still picture.
In this case, the utility factor of the recording area can improve. However, one restriction is imposed when rewriting voice information. Namely, since image information recorded a latter portions need to be protected, new information to be recorded can not be longer than the formerly recorded voice information.
Moreover, when unnecessary voice information is erased, blank areas which were the prior voice information recording areas A1, A2 . . . are present. However, since the length of each area is different from another, if image information is recorded in the areas, the utility factor becomes low and the address management becomes complicated.
In the mean time, when rewriting information by the use of the signal format for CD, a piece of information recorded in a target physical sector is actually divided into a plurality of pieces and recorded in various sectors on the disk by CIRC. Therefore, it is difficult to rewrite information by only rewriting the desired sector. In fact, data desired to be rewritten and data recorded just before and after the desired data are stored in the same sector on the disk, and the connection or relationship of error correction is given between the respective data. Therefore, it is difficult to keep the connection in the case where only the desired data is rewritten (see Japanese published Patent Official Gazette, Tokukaihei 1-55787 for more details). In other words, all the recording information is recorded successively in the CD format. However, if a part of recorded data is rewritten, the connection of error correction between the data and data recorded just before and after the recorded data is lost in the vicinity of the recording start and end positions of the rewritten data, causing frequent reproduction errors. The reasons for this is that since the minimum access unit to the information recording position is a sector, sectors to which the user can not access exist in front and after the rewritten information. As a result, the utility factor of the disk decreases.
In order to prevent such reproduction errors from occurring, for example, additional sectors wherein dummy data is recorded may be provided before and after data to be actually recorded and reproduced. The dummy data comprises parity codes for correcting errors which may occur in the leading and ending parts of the data. For example, in the case of the CD format, to demonstrate the full correction ability of CIRC, i.e. to transmit codes in the non-complete interleaving method, 105 frames are required. Therefore, it is desirable to provide (105/98).apprxeq.1.07 sectors each before and after a sector comprising 98 frames. i.e. two additional sectors each practically. The additional sectors can be used as sectors where a Phase Locked Loop (PLL) can execute pull-in operations. However, providing the additional sectors results in the decrease in the utility factor of the disk.
In order to carry out address management or the like easily when rewriting information, every predetermined numbers of the sectors form a block, and for example two additional sectors described above may be provided at the lead and end of each block so as to rewrite information block by block (hereinafter referred to as by the block unit).
However, if the additional sectors are provided for every block, when high-volume data is recorded in a number of sectors, the respective additional data needs to be recorded in each additional sector provided for the blocks. Consequently, the utility factor of the disk and the data transmission speed drop.
To reduce the drop in the utility factor of the disk caused by providing additional sectors to the minimum degree, the number of sectors forming the minimum unit of rewritten a piece of information (hereinafter referred to as block) should be increased. As a result, the utility factor of the disk comes close to the primary utility factor of CDs. However, it is unsuitable to form blocks composed of sufficiently large numbers of sectors for every kind of information, for example low-volume data such as text information, and also the time taken for recording is wastefully prolonged.
Arranging the sizes (the number of sectors per block) of the blocks as above has both merits and demerits according to the content of information to be recorded. When the CLV format for CD is adopted, if a recording operation and a reproduction operation for verification are repeatedly performed by the block unit, the wait time between the completion of the recording operation and the start of the reproduction operation for verification is undesirably prolonged at an outer part of the disk, especially when the length of one block is shorter than the time taken for one disk rotation.
In order to explain the above, the time chart of FIG. 22 shows an example of a recording operation and a reproduction operation for verification successively performed by the block unit by using a conventional disk whereon recording can be executed in the CLV method. The periods shown by t.sub.o and t.sub.n of the figure indicate time required for each rotation of the disk at respective information positions, W.sub.o indicates a recording operation to block No. 0 located in the innermost portion of the disk, W.sub.n a recording operation to block No. n located in the outermost portion thereof, and R.sub.n a reproduction operation for verification of block No. n after the recording operation.
Wait time for rotating the disk to proceed to the reproduction operation for verification after the recording operation is obtained by subtracting the operation time W.sub.o (or W.sub.n) from the time t.sub.o (or t.sub.n) required for one disk rotation. It can be seen from FIG. 22 that the wait time for rotating the disk in an outer part of the disk shown in (b) is longer than the wait time in an inner part thereof shown in (a). In other words, the information volume per time, i.e the data transmission rate, decreases at outer parts of the disk.
To a host device (so-called personal computer) for managing various types of information, in general it is desirable to perform a recording or a reproducing operation by the sector unit or the block unit like the conventional floppy disks and hard disks. However, in the case of the above format, additional sectors, for example two sectors, are respectively required before and after the sectors in each recording operation. Therefore, it is necessary to transmit sectors corresponding to the additional sectors together. Besides, in case of rewriting information, it is necessary to manage both sectors which can be used as data areas and additional sectors which can not be used, thereby causing the management to be complicated.
In the case of a high volume of information such as digital and music information, large numbers of sectors are required for recording the information. Therefore, even in case additional sectors are not provided, only a minor problem occurs, i.e. the leading and ending parts of the information are slightly broken. Namely, in the case of the music information, the information is not affected much aurally. On the contrary, in the case of digital information or the like where small numbers of sectors are required for recording the information, generally additional sectors need to be provided. Thus, various problems arise as described above.